Heretofore, many printed wiring boards have been used, in each of which a solder resist pattern, which is a pattern-shaped solder resist film, is formed on a substrate having a wiring provided on the upper surface thereof. In the printed wiring boards, finer solder resist patterns have been demanded with the reduced sizes of electronic devices and the increased densities of the patterns in electronic devices.
As the method for forming a fine solder resist pattern, a method in which a solder resist composition is applied by an inkjet mode has been proposed. In an inkjet mode, the number of steps is reduced compared with the case where a solder resist pattern is formed in a screen printing mode. Therefore, in an inkjet mode, a solder resist pattern can be formed easily and highly efficiently.
In the case where a solder resist composition is applied by an inkjet mode, it is required that the viscosity of the solder resist composition is low to a certain extent during the application of the solder resist composition. Recently, on the other hand, an inkjet device that can be warmed to 50° C. or higher during printing has been developed. When a solder resist composition is warmed to 50° C. or higher in an inkjet device, the viscosity of the solder resist composition can become relatively low, and therefore the dischargeability of the solder resist composition with the inkjet device can be further improved.
A solder resist composition that can be applied by an inkjet mode is disclosed in Patent Document 1. In Patent Document 1, a curable composition for inkjet which comprises a monomer having both a (meth)acryloyl group and a thermally curable functional group, a photoreactive diluent having a weight average molecular weight of 700 or less and a photopolymerization initiator is disclosed. The viscosity of the curable composition for inkjet at 25° C. is 150 mPa·s or less.